1. Field of the Invention
The present invention relates to a method for processing a peripheral portion of a thin plate, such as a silicon wafer and an apparatus therefor.
2. Description of the Related Art
A shock (impact) load is applied to a peripheral portion of a silicon wafer when a lapping step or a double side polishing step is carried out in a process of manufacturing silicon wafers. A shock load is applied to a peripheral portion of a wafer in a process of manufacturing semiconductor elements because of a thermal stress caused by a heating and cooling treatment between room temperature and one thousand and several hundred degrees centigrade or because of a film forming treatment, such as an oxidation. Further, a shock load is applied to a peripheral portion of a wafer locally and frequently because a wafer is positioned, a wafer is transferred inside an apparatus, a wafer is transferred between one apparatus and another, a wafer is supported or the like by using a peripheral portion of the wafer in the process of manufacturing silicon wafers and in the process of manufacturing semiconductor elements.
When the shock load is applied to a peripheral portion of a wafer locally, the peripheral portion of the wafer is liable to be chipped off. Because the Si wafer which is a material for semiconductor elements is made of a silicon and is a single crystal, the wafer has a cleavage depending on a crystal orientation thereof and is brittle. When the wafer is chipped off, small fragments thereof fly. Because the small fragments adhere to the surface of the wafer, on which the semiconductor elements are formed, the characteristics of the semiconductor elements and the yield thereof are deteriorated.
The peripheral portion of the wafer has been chamfered in order to avoid or relieve these problems according to an earlier development.
Next, the typical three types of the chamfering apparatus will be explained below.
The first chamfering apparatus is a formed chamfering apparatus shown in FIG. 7. The chamfering apparatus 100 comprises a grinding wheel 101 (a so-called formed grinding wheel) having a groove of which shape is the same as that of a chamfered portion. The wafer W is held on the holding table 102 by using a vacuum chuck. In this chamfering apparatus 100, the grinding wheel 101 is pushed to the wafer W by applying a constant load thereto in order to process the peripheral portion of the wafer W. According to the chamfering apparatus 100, the shape of the chamfered portion of the wafer W is determined by the shape of the groove of the grinding wheel 101.
The second chamfering apparatus is a copy chamfering apparatus shown in FIG. 8. The chamfering apparatus 200 comprises a grinding wheel 201 having a groove 201a of which width is larger than the thickness of the wafer W. The wafer W is sandwiched by a pair of holding bodies 202 and 203 disposed at upper and lower positions of the wafer W to be sandwiched in order to hold the wafer W. In the chamfering apparatus 200, a copy model 204 is disposed on the same axis as the upper holding body 202. The copy model 204 and the upper holding body 202 rotate together and move in a vertical direction. A copy roller 205 is disposed on the same axis as the grinding wheel 201. The copy roller 205 and the grinding wheel 201 rotate independently of each other.
The process of chamfering the peripheral portion of the wafer is carried out by using the chamfering apparatus 200 as follows. That is, after the wafer W was sandwiched, the copy roller 205 moves in a direction of the copy model 204. The copy roller 205 and the copy model 204 roll in order to contact with each other. While the copy roller 205 moves, the grinding wheel 201 contacts the wafer W in order to start chamfering the peripheral portion of the wafer W. In the chamfering process, the peripheral portion of the wafer W is processed by rotating the wafer W by one rotation. The wafer W is moved upwardly and is rotated by one rotation in order to chamfer the upper surface of the peripheral portion of the wafer W. The wafer W is moved downwardly and is rotated by one rotation in order to chamfer the lower surface of the peripheral portion of the wafer W.
In the chamfering apparatus 200, because the diameter of the grinding wheel 201, which is measured on the basis of the bottom of the groove 201a is the same as that of the copy roller 205, the diameter of the wafer W is the same as that of the copy model 204. The upper surface of the peripheral portion of the wafer W is processed by the upper wall of the groove 201a. The lower surface of the peripheral portion of the wafer W is processed by the lower wall of the groove 201a. As a result, the shape of the upper part of the chamfered portion corresponds to that of the upper wall of the groove 201a. Similarly, the shape of the lower part of the chamfered portion corresponds to that of the lower wall of the groove 201a. Further, the width of the chamfered portion is determined by the positions in which the wafer W is disposed when the wafer W is moved upwardly and when the wafer W is moved downwardly.
The third chamfering apparatus is an NC (numerical control) chamfering apparatus which is not shown in the drawings. The chamfering apparatus carries out the control of the relative positions of the wafer and the grinding wheel not by using the copy roller and the copy model like the copy chamfering apparatus, but by the NC control. The process of chamfering the peripheral portion of the wafer is carried out similarly to the copy chamfering apparatus.
The function of the chamfered portion of the wafer is not only that the wafer is prevented from being chipped off. In particular, in case of a wafer for making an epitaxial wafer, the chamfered portion of the wafer prevents an extraordinary growth of an Si single crystal at the peripheral portion of the wafer. Further, the chamfered portion of the wafer drains liquid during a spin coat in a resisting step. It is decided by the cross-sectional shape of the chamfered portion of the wafer (hereinafter, referred to as xe2x80x9cchamfer shapexe2x80x9d) and by the size thereof which function of the chamfered portion is superior to another. It is necessary to select the chamfer shape and the size of the chamfered portion suitably by considering which function is important. For example, the chamfer shape is a semicircular shape, a trapezoidal shape, a shape in which an end of a trapezoid is round or the like. There are various sizes of the chamfered portion.
However, in the three types of chamfering apparatus, because the chamfer shape is determined by the shape of the groove of the grinding wheel, it is necessary that one grinding wheel should be changed for another having a different groove from one grinding wheel when the shape of the chamfered portion is changed. Several types of grinding wheels must be prepared in order to change one grinding wheel for another. It is troublesome to change one grinding wheel for another. Further, there is a problem that a chamfering apparatus cannot be operated while one grinding wheel is changed for another.
The present invention was developed in view of these problems.
An object of the present invention is to provide a processing method for processing several types of chamfered portions or the like without changing one tool for another and a processing apparatus therefor.
That is, in accordance with one aspect of the present invention, the method for processing a peripheral portion of a thin plate, comprises the steps of; contacting the thin plate with a processing part of a tool, which has a round free end and projects to the thin plate in order to process the contacted peripheral portion of the thin plate, and moving at least one selected from the tool and the thin plate in a direction of the other, which is parallel to a main surface of the thin plate and in a direction of the other, which is normal to the main surface of the thin plate, in order to change one contacting point between the peripheral portion of the thin plate and the processing part of the tool to another contacting point and to process the changed contacting point of the peripheral portion of the thin plate.
In the specification, the word xe2x80x9cprocessxe2x80x9d means the process of the chamfered portion, that is, making the chamfered portion and polishing the chamfered portion, if other meanings of the word xe2x80x9cprocessxe2x80x9d are not given especially.
According to the method for processing the peripheral portion of the thin plate, because the step of contacting the thin plate with a processing part of a tool, which has a round free end and projects to the thin plate in order to process the contacted peripheral portion of the thin plate, and the step of moving at least one selected from the tool and the thin plate in a direction of the other, which is parallel to a main surface of the thin plate and in a direction of the other, which is normal to the main surface of the thin plate, in order to change one contacting point between the peripheral portion of the thin plate and the processing part of the tool to another contacting point and to process the changed contacting point of the peripheral portion of the thin plate, are carried out, the peripheral portion of the thin plate can be processed by using each point of the processing part of the tool. As a result, the chamfered portions having various shapes can be properly made by one tool. When the tool for making the chamfered portion is changed for one for polishing the chamfered portion, the chamfered portions having various shapes can be polished. Because a load is dispersed into a whole processing part without applying it to a specific position of the tool, a life of the tool can be longer.
The moving step may be carried out by moving at least one selected from the tool and the thin plate further in a direction normal to the direction of the other, which is parallel to the main surface of the thin plate and to the direction of the other, which is normal to the main surface of the thin plate.
According to the method of processing the peripheral portion of the thin plate, even though the peripheral portion of the thin plate is composed of a linear form, the peripheral portion of the thin plate can be processed.
The processing part of the tool may comprise a flat portion of which upper and lower surfaces are parallel to each other.
A gentle slope part which is a boundary part between the chamfered portion and the main surface of the thin plate can be properly processed.
A thickness of the processing part may be two or more times larger than that of the thin plate. A radius of curvature of the round free end of the processing part may be larger than a half of a thickness of the flat portion of the processing part. The tool may have a cylindrical shape and the processing part attached to a circumferential portion of the tool has a ring shape.
In accordance with another aspect of the present invention, the method for processing a peripheral portion of a thin plate, comprises the steps of; contacting the thin plate with a processing part of a tool, which has a groove having a round bottom so as to surround the peripheral portion of the thin plate with the processing part from three different directions from one another, in order to process the contacted peripheral portion of the thin plate, and moving at least one selected from the tool and the thin plate in a direction of the other, which is parallel to a main surface of the thin plate and in a direction of the other, which is normal to the main surface of the thin plate, in order to change one contacting point between the peripheral portion of the thin plate and the processing part of the tool to another contacting point and to process the changed contacting point of the peripheral portion of the thin plate.
The opening width of the groove is not less than 1000 xcexcm preferably when the thicknesses of the thin plates are from 500 xcexcm to 900 xcexcm. It is necessary that the opening width of the groove is not less than 1000 xcexcm in order to process these thin plates by using one tool.
Because the step of contacting the thin plate with a processing part of a tool, which has a groove having a round bottom so as to surround the peripheral portion of the thin plate with the processing part from three different directions from one another, in order to process the contacted peripheral portion of the thin plate, and the step of moving at least one selected from the tool and the thin plate in a direction of the other, which is parallel to a main surface of the thin plate and in a direction of the other, which is normal to the main surface of the thin plate, in order to change one contacting point between the peripheral portion of the thin plate and the processing part of the tool to another contacting point and to process the changed contacting point of the peripheral portion of the thin plate, are carried out, the peripheral portion of the thin plate can be processed by using each point of the processing part of the tool. As a result, the chamfered portions of the thin plate having a thickness smaller than the opening width can be properly made by one tool.
The moving step may be carried out by moving at least one selected from the tool and the thin plate further in a direction normal to the direction of the other, which is parallel to the main surface of the thin plate and to the direction of the other, which is normal to the main surface of the thin plate.
According to the method of processing the peripheral portion of the thin plate, even though the peripheral portion of the thin plate is composed of a linear form, the peripheral portion of the thin plate can be processed.
A depth of the groove is larger than a width of a chamfered portion of the thin plate.
A gentle slope part which is a boundary part between the chamfered portion and the main surface of the thin plate can be properly processed.
In accordance with another aspect of the present invention, the apparatus for processing a peripheral portion of a thin plate, comprises; a tool having a processing part which has a round free end and projects to the thin plate, a contacting device for contacting the thin plate with the processing part of the tool in order to process the contacted peripheral portion of the thin plate, and a moving device for moving at least one selected from the tool and the thin plate in a direction of the other, which is parallel to a main surface of the thin plate and in a direction of the other, which is normal to the main surface of the thin plate, in order to change one contacting point between the peripheral portion of the thin plate and the processing part of the tool to another contacting point and to process the changed contacting point of the peripheral portion of the thin plate.
According to the apparatus for processing the peripheral portion of the thin plate, the peripheral portion of the thin plate can be processed by using each point of the processing part of the tool. As a result, the chamfered portions having various shapes can be properly made by one tool. When the tool for making the chamfered portion is changed for one for polishing the chamfered portion, the chamfered portions having various shapes can be polished. Because a load is dispersed into a whole processing part without applying it to a specific position of the tool, a life of the tool can be longer.
The moving device may move at least one selected from the tool and the thin plate further in a direction normal to the direction of the other, which is parallel to the main surface of the thin plate and to the direction of the other, which is normal to the main surface of the thin plate.
According to the apparatus for processing the peripheral portion of the thin plate, even though the peripheral portion of the thin plate is composed of a linear form, the peripheral portion of the thin plate can be processed.
The processing part of the tool may comprise a flat portion of which upper and lower surfaces are parallel to each other.
A gentle slope part which is a boundary part between the chamfered portion and the main surface of the thin plate can be properly processed.
A thickness of the processing part may be two or more times larger than that of the thin plate. A radius of curvature of the round free end of the processing part may be larger than a half of a thickness of the flat portion of the processing part. The tool may have a cylindrical shape and the processing part attached to a circumferential portion of the tool has a ring shape.
In accordance with another aspect of the present invention, the apparatus for processing a peripheral portion of a thin plate, comprises; a tool having a processing part which has a groove having a round bottom, a contacting device for contacting the thin plate with the processing part of the tool so as to surround the peripheral portion of the thin plate with the processing part from three different directions from one another, in order to process the contacted peripheral portion of the thin plate, and a moving device for moving at least one selected from the tool and the thin plate in a direction of the other, which is parallel to a main surface of the thin plate and in a direction of the other, which is normal to the main surface of the thin plate, in order to change one contacting point between the peripheral portion of the thin plate and the processing part of the tool to another contacting point and to process the changed contacting point of the peripheral portion of the thin plate.
According to the apparatus for processing the peripheral portion of the thin plate, the peripheral portion of the thin plate can be processed by using each point of the processing part of the tool. As a result, the chamfered portions of the thin plate having a thickness smaller than the opening width can be properly made by one tool.
The moving device may move at least one selected from the tool and the thin plate further in a direction normal to the direction of the other, which is parallel to the main surface of the thin plate and to the direction of the other, which is normal to the main surface of the thin plate.
According to the apparatus for processing the peripheral portion of the thin plate, even though the peripheral portion of the thin plate is composed of a linear form, the peripheral portion of the thin plate can be processed.
A depth of the groove is larger than a width of a chamfered portion of the thin plate.
A gentle slope part which is a boundary part between the chamfered portion and the main surface of the thin plate can be properly processed.
According to the present invention, because the step of contacting the thin plate with a processing part of a tool, which has a round free end and projects to the thin plate in order to process the contacted peripheral portion of the thin plate, and the step of moving at least one selected from the tool and the thin plate in a direction of the other, which is parallel to a main surface of the thin plate and in a direction of the other, which is normal to the main surface of the thin plate, in order to change one contacting point between the peripheral portion of the thin plate and the processing part of the tool to another contacting point and to process the changed contacting point of the peripheral portion of the thin plate, are carried out, the peripheral portion of the thin plate can be processed by using each point of the processing part of the tool. As a result, the chamfered portions having various shapes can be properly made by one tool. When the tool for making the chamfered portion is changed for one for polishing the chamfered portion, the chamfered portions having various shapes can be polished.